The present invention relates to an improved apparatus for high-speed continuous casting of high quality thin steel slabs.
Conventionally, the continuous casting of the so-called "thin slabs" of steel, up to 80 mm thick, has been subject to quality problems, especially for casting at high speed, e.g. above 4.5 m/mm.
Such problems result in flaws in the slab surface, i.e., the shell, which is formed in the mould, as follows:
longitudinal cracks due to the trapping of casting powders; PA1 longitudinal and transversal cracks due to a lack of lubricating and insulating film formed by "slag" (i.e., the product of casting powders being melted and resolidified); PA1 longitudinal cracks due to thermal stresses; and PA1 longitudinal cracks due to the copper cooling surfaces of the mould being discontinuous.
These problems typically affect special steels, but could be at least partially solved by reducing the casting speed. However, reducing casting speed would lower productivity and accordingly reduce plant efficiency. Another possible solution to the above problems could be to use an electromagnetic device, called "EMBR" (ElectroMagnetic Brake Ruler), capable of flattening the liquid steel waves rippling along the meniscus inside of the mould. However, an EMBR is very expensive and would only partially solve the aforementioned problems. Additionally, other problems arise from the geometrical and flow conditions occurring inside the mould, resulting in a reduction of the operating life of the casting nozzle (which is dipped in the liquid metal and is usually called a "submerged nozzle") and in a reduction of process efficiency.
From the above discussion it should be clear that the quality control problems can not be solved in a systematic and satisfying way by independently concentrating on any one of the mould, the submerged nozzle and the mould oscillating unit. The above three elements are so interconnected in the continuous casting process that to solve the above-mentioned quality problems, the three elements must be treated together. Thus, to find an effective solution it is important to concentrate on the mould, the submerged nozzle, and the mould oscillating unit as a single group.